In recent years "chip carriers" have emerged as a promising high-volume device packaging technique. In its simplest form a chip carrier is a substantially square, relatively thin, article having a cavity with bonding pads therein which are connected by a plurality of electrically conductive leads that extend through walls of the carrier, along the side walls, and terminate on the underside of the carrier. A semiconductor circuit chip is placed in the cavity, connected to the bonding pads and a cover is placed over the cavity which may be used to hermetically seal the chip therein.
A multitude of such chip carriers may be soldered to conductive lands on the surface of a Printed Circuit Board (PCB). The conductive lands are aligned with the leads on the underside of the chip carrier, at least one of which will have predeposited amounts of solder thereon, the leads and lands are then placed in contact and the solder reflowed to effect a bond.
Various techniques have been used to reflow the solder. Condensation soldering and various types of belt furnaces have proven effective for soldering the leads of chip carriers to the lands on a PCB or other metallized conductor patterns on a substrate. However, when one or more of the chip carriers has to be soldered in a densely packed array or has to be removed for replacement or repair, the condensation and belt furnace techniques melt solder connections of neighboring chip carriers. This can also cause alloying and possible embrittlement of those solder connections. Additionally, other chip carriers or components on the PCB may undesirably move or be exposed to damage due to excessive heat.
Heating tools have been devised to clamp all four sides of a chip carrier to reflow the solder and remove the carrier from the PCB. However, such direct contact with a heating tool can damage the carrier and/or PCB. Direct contact also results in some flux adhering to the tool, making controlled release of the chip carrier difficult. All soldering connections must be molten at the time of chip carrier removal or during replacement reflow, a condition difficult to achieve with contact tools.
One solution to the problem is described in copending patent application Ser. No. 80,816, filed on Oct. 1, 1979. This application describes an apparatus for simultaneously soldering terminals on a multi-sided article having at least one terminal on each side, to mating land areas on the surface of a metallized substrate. Hot gas is directed through a plurality of angled slots in a housing onto the terminals and land areas to form a bond therebetween. Although such a technique is most effective in forming a bond, it has been found that a substantial amount of heat is imparted to the PCB due to direct and/or deflected impingement of the hot gas thereon. Such heat can cause undesirable cracking, degradation and/or deformation of the PCB in the vicinity of the chip carrier.
Accordingly, there is a need for a universal soldering tool that is capable of soldering or desoldering chip carriers or the like to the surface of metallized substrates without significant heat being applied to the substrate or other components thereon.